True, Roberts’s opinion, joined by the court’s four doubtless relieved liberals, struck down the buffer as a violation of the free-speech rights of pro-life activists who seek to converse with women who might be seeking abortions.

But the crucial element in the opinion -- the one that got the liberals on board and enraged the conservatives -- is that Roberts said the law was neutral with respect to the content of speech as well as the viewpoint of the speakers.

That conclusion protected the possibility of other laws protecting women seeking abortions that pay more attention to what Roberts said was missing here, namely proof that the law was narrowly tailored. For the liberals, that was enough to get on board.

To understand the weirdness of the case, and how it is that striking down the buffer law is still a victory for liberals, you need Free Speech 101, which is luckily very simple.

Speech in a traditional public forum such as a sidewalk is protected by the First Amendment. But the government can regulate the time, place and manner of the use of public streets.

The only requirement the government must satisfy is to show that the law is “narrowly tailored to serve a significant governmental interest” and that it leaves open “ample alternative channels for communication.”

This standard is challenging to meet, but by no means impossible. Consider a law banning sound trucks blaring on your street at night.

It would probably be constitutional, because the government has a significant interest in the citizens’ sleep, and there would be plenty of other times for sound trucks to operate, leaving ample alternatives for communication. It is this standard that Roberts applied to the buffer zone -- and that will therefore be applied to other, similar buffer laws in the future.

If, however, a government law burdens speech based on its content, not its time, place or matter, the law is very different. Then the law would be subject to what’s called “strict scrutiny,” which would require that there be not merely a significant governmental interest but a compelling one.

In addition, the government would have to show that it was using the least restrictive means possible. In practice, when it comes to the First Amendment, applying strict scrutiny is almost always enough to kill the law -- as the saying goes, such scrutiny is “strict in theory, fatal in fact.”

If the law favors one viewpoint over another, strict scrutiny would also apply -- and the buffer law would almost certainly go down.

Justice Antonin Scalia, joined by Justice Clarence Thomas and Justice Anthony Kennedy, wrote separately to insist that the buffer law was content-based because it was aimed at anti-abortion speech.

Why else, Scalia asked, was the law aimed at spaces outside facilities where abortions were being performed? He would have found the law to be content-based and applied strict scrutiny.

Justice Samuel Alito wrote separately on his own to say that the law discriminated on the basis of viewpoint, because it allows employees of the clinic inside the zone but not other members of the public except passers-by.

This, he said, was intended to discriminate against anti-abortion speech.

In his opinion, Roberts answered both charges. First, he said that, while the law obviously would be more likely to restrict abortion-related speech than other speech, it was still neutral with respect to content.

The law was intended, he said, to increase public safety around public health facilities, and any disproportionate effect on certain speech was “incidental.”

He accepted Massachusetts’s argument that law was not named at protecting people’s feelings but at public safety.

Then, responding to Alito, Roberts said that the exemption for clinic employees need not be understood as a carve-out for escorts helping women seeking abortions.

It would also include maintenance workers shoveling snow. As a result, the law was also viewpoint neutral.

Having dispensed with these arguments, Roberts went on to say that the law was not narrowly tailored because it banned substantially more speech than necessary to achieve the government’s interests.

Here Roberts insisted, in terms that cannot have made all the liberals very happy, that people seeking to speak outside abortion clinics were not merely protesters, but were activists seeking “personal, caring, one-on-one conversations.” The buffer zone robbed them of that opportunity, and was therefore unconstitutional.

Finally, Roberts gave the Commonwealth of Massachusetts a road map of what it would be permitted to do, consistent with the Constitution, to protect public safety outside facilities that perform abortions.

Massachusetts could, he said, make it a crime to block entry or exit from the clinics or to obstruct anyone seeking health care. It could criminalize harassing anyone within 15 feet of a health-care facility, as New York City does.

It could also use existing local ordinances that prohibit anyone from blocking the sidewalk or soliciting others while walking on the street. Finally, the commonwealth could seek an injunction against any group that violated the rules.

No wonder the conservative justices were up in arms. To them, the buffer law should have been struck down as an unjustifiable intervention on behalf of one side in the cultural debate about abortion. Roberts steadfastly refused to acknowledge this.

By treating the lawmakers as well as the pro-life activists as well-intentioned and law-abiding, he was offering a kind of moderate legal-cultural solution to the abortion debate as it takes place outside clinics.

Roberts’s concession to the liberals assures that courts will uphold the enforcement of laws such as those he cited to protect clinics. But the most important part of the opinion is that it is actually, truly centrist.

The question of whether Roberts is a true moderate has not yet been answered, and next week may well bring truly conservative opinions from him. But certainly the case that Roberts is a diehard conservative remains unproved.

Feldman is an assistant professor of finance at Stoney Brook University and a freelance writer for a number of finance and business publications.